Method for configuring a network termination unit

ABSTRACT

The invention relates to a method for configuring a network termination unit for the packet-by-packet asynchronous transfer mode transmission of data. According to said method data subdivided into cells and assembled into packets are transmitted either at a constant data rate (CBR), for example in the case of voice or video data, or at a non-constant data rate (UBR). The data cells or packets are received and transmitted via the network termination unit, which constitutes an interface between a transmission line and data terminal. The number of data cells contained in each transmitted or received data packet is determined in the network unit ( 10 ) and from this number it is determined whether the ATM connection is carried out at a constant (CBR) or non-constant (UBR) data rate. The data packets of a CBR connection have processing priority over the data packets of a UBR connection.

The invention relates to a process for configuring a network terminationunit for asynchronous packet ATM (Asynchronous Transfer Mode)transmission of data, the data divided into cells and assembled intopackets being transmitted either at a constant data rate (CBR, ConstantBit Rate) or at a non-constant data rate (UBR, Unspecified Bit Rate),and the data cells of packets being received and sent over the networktermination unit, which represents an interface between a transmissionline and a data end device.

To increase efficiency, the principle of packet switching is applied inmany data nets in the transmission of data. The data to be transmittedis divided, at node points defined for the purpose, into definedpackets, is provided with an address and additional auxiliaryinformation such as error protection, and is transmitted to the nextnode in a packet-switched manner independently of the origin anddestination of the data; the packets can be intermediately stored ineach node until they are transmitted. A service designed for thispurpose is, e.g., SDH (Synchronous Digital Hierarchy), in whichstandardized interfaces and multiplex systems make possible transmissionrates of 155 Mbit/s. A further development thereof is represented by theATM (Asynchronous Transfer Mode) kind of transmission, by means of whichthe data to be transmitted are split up into cells of fixed length andasynchronously multiplexed. In addition, these cells are combined intostandardized packets.

The great advantage of ATM is that the available bandwidth can be usedin the best possible manner at any given time. For this purpose,different kinds of transmission rates can be established. Thus, forexample, a choice can be made between a constant transmission rate CBRand a non-constant transmission rate UBR, in order to be able to fulfillvarious requirements. Constant bit rate (CBR) is always required when adelay of the packets by predetermined delay times could have troublesomeeffects, as is the case for video or speech transmissions. UBRtransmission can be generally used in data traffic, since a change ofthe data transmission rate plays no part for this purpose. Therefore, atnodes within the data transmission path, those data packets which aresent in CBR mode are given preference over those transmitted in UBRmode, in order to be able always to ensure the constant transmissionrate for the CBR packets.

In an ATM network which extends via a two-wire circuit, e.g., asubscriber line circuit, to a subscriber's telephone end device, as isrealized with broadband transmission applications, for example inconnection with ADSL (Asynchronous Digital Subscriber Line), a networktermination unit or NT unit over which the data are received and sentexists for each subscriber. In the mentioned ADSL systems, datareception is in the foreground, since the subscriber usually calls up ahigh information content via the subscriber line circuit, e.g. for homevideo or internet applications. The subscriber can have various kinds ofNT units at his disposal, as for example an ATM interface with 25.6Mbit/s. Other standards also exist besides this, such as, e.g.,Ethernet, but the present invention is not directed toward these.

There are differently equipped ATM NT units which differ from each otherby the implemented intelligence. A particular feature consists of theprovision of a connection between the NT unit and a so-called elementmanager in the ATM network on a higher information layer whichcorrespondingly configures the NT units. This configuration datacontains, among other things, information concerning the kind of datatraffic (Quality of Service, QoS), e.g., CBR or UBR, related to theaddresses of the individual cells (VPI/VCI). The respectiveconfiguration thereby decides how the received data is to be treated.Thus the CBR packets can be granted priority, since these must notundergo a large or variable delay. They are therefore conducted throughsmall cell buffers, and due to this are limited in their peaktransmission rate. UBR packets can appear in large bursts and aretherefore to be conducted through large packet buffers, in order toavoid a loss of packets or cells.

Additionally, the so-called EPD (Early Packet Discard) process can beapplied to the data stream, and reduces the number of false or lostcells, thereby increasing the data throughput, e.g. for datatransmissions (TCIP/IP).

If this remote configuration does not take place, or takes place only toa limited extent, considerable data losses can occur when UBR packetsare treated as CBR packets and, because of the small buffer memory, alarge part of the data cannot be buffered. A further disadvantage of theconventional configuring process consists in that heretofore nogenerally accepted protocol has been defined for this purpose, andmatching difficulties for this reason arise again and again.Furthermore, remote configuration also increases complexity and thus thecosts of an ATM transmission.

The invention therefore has as its object to provide a configurationprocess of the kind stated at the beginning, with which an effectiveallocation of ATM packets with different transmission modes and thecorresponding buffers can be directly performed in a network terminationunit.

This is attained according to the invention in that the number of thedata cells contained in each sent or received data packet is determinedin the network unit (10), and from this it is determined whether an ATMconnection with constant (CBR) or non-constant (UBR) data rate ispresent; and in that the data packets of a CBR connection are processedwith higher priority than the data packets of the UBR connection.

In this manner, each network termination unit can undertake, completelyindependent of the rest of the network, an analysis of how the incomingor outgoing data traffic is to be treated, so that data losses and theexpense of complex protocols can be avoided.

Different adaptation layers (AAL) are defined for the ATM datatransmission, according to the application: for CBR connections, usuallyAAL1 or AAL5, and for UBR connections, AAL5. Network termination unitsknown heretofore cannot automatically determine the kind of transmissionpresent at the time, and therefore have to be remotely configured overthe ATM network, resulting in an increased expense.

In a process in which adaptation layers with different packet length aredefined for the transmission of the data packets, the networktermination unit can, in a development of the invention, determine thekind of data connection, in that on determination of a data packet whichcontains more than a predeterminable number of cells greater than two,preferably three cells, a UBR packet is detected, and in all other casesa CBR data packet is detected; and in that the ATM connection iscorrespondingly classified as a UBR or a CBR connection.

A preferential treatment of the CBR transmission can thus be undertaken,in a further development of the invention, in that at the beginning oftransmission a CBR connection is always assumed as the initial value.

In order to further ensure that a successive transmission of datapackets is carried out in one of the two transmission modes, in a datastream incoming to the network unit or sent out from the said unit, itcan be provided according to a further embodiment example of theinvention that the presence of a UBR or CBR connection is determinedonly after the evaluation of the results of a predeterminable number ofdata packets.

Finally, if a UBR or CBR connection is determined in the networktermination unit, according to a variant of the invention it can beprovided that the data packets by the network termination unit as datapackets of a UBR connection are fed to a buffer with relatively highstorage capacity and the data packets detected by the networktermination unit as data packets of a CBR connection are fed to a bufferwith relatively low storage capacity.

According to a further feature of the invention, it can be provided thaton establishing a UBR connection, the network termination unit canoptionally be set in the EPD (Early Packet Discard) mode, whereby anoverflow of the buffer is prevented.

The invention furthermore relates to a network termination unit for theasynchronous ATM transmission of data in packets (Asynchronous TransferMode), by means of which the data divided into cells and assembled intopackets with several cells can be sent and received with constant (CBR)and also non-constant (UBR) data rate, a buffer with relatively largecapacity allocated to the UBR data, and a buffer with relatively smallcapacity allocated to the CBR data are provided, which can in particularserve for the application of the process according to the invention.

The invention has as its object to provide a network termination unitwhich is capable of undertaking an automatic configuration according tothe kind of data transmission.

This attained according to the invention in that it comprises a devicefor the determination of the number of data cells contained in each datapacket which undertakes a classification, corresponding to thedetermined number of data cells, of the ATM connection present, andaccording to this classification deflects the data packets either intothe buffer with relatively small capacity allocated to the CBR data orinto the buffer with relatively large capacity allocated to the UBRdata.

The mode in which the transmission at the present time is carried outcan be determined in this manner for an existing data connection, sothat a corresponding effect on the network termination unit can becarried out.

The invention will be described in more detail hereinbelow using theembodiment example shown in the accompanying drawings.

FIG. 1 is a schematic diagram of an ATM cell;

FIG. 2 is a schematic diagram of an AAL5 packet;

FIG. 3 is a schematic diagram of the cell head of the last cell of anAAL5 packet, and

FIG. 4 is a block circuit diagram of an ATM data transmission systemwith an embodiment of the network termination unit according to theinvention.

FIG. 1 shows a standardized ATM cell 1, as used for data transmission.In consists of a cell head or header 2 with 5 bytes and a use data field3 having a length of 48 bytes. Cells of this kind are transmittedasynchronously, and thus without previously fixed allocated places, bymultiplexing. The identifier (VPI/VCI) contained in the header isevaluated for the switching of the cells between successive transmissionsections, by means of which it can be determined which ATM connection ispresent at a given time.

During the transmission of data between a data source and a data sink,different adaptation layers (AAL adaptation layers), e.g., AAL1, AAL5,can be allocated to each connection in the ATM process, respectivelyseveral cells 1, 1′ (up to 1365 cells corresponding to an effective bitrate of 64 kB) are assembled into a packet and are transmitted (FIG. 2).Each header of the last cell of a packet has a special identifier(VCI/VPI) from which an AAL5 packet can be recognized. If such anidentifier appears, the adaptation layer is defined as AAL5. However, nounique identification of the kind of transmission (QoS, Quality ofService) can be thereby determined, since CBR connections can also bepackaged in AAL5 packets.

Typical applications of CBR (Constant Bit Rate) connections are realtime transmissions, accordingly speech and video transmissions, e.g.,video conferences, where a delay should take place only within givenlimits. AAL1 packets are chiefly used for CBR, but nevertheless no clearallocation can result from this criterion, since a CBR transmission isoften carried out in which only a single, or very few, ATM cells aresent in an AAL5 packet. The time delay arising from the packing andunpacking of the ATM cells can thereby be kept small. However, more thanthree ATM cells per packet are not used in a CBR transmission.

In contrast to this, UBR (Unspecified Bit Rate) is chiefly used for puredata transmission and is always carried out using AAL5 packets whichcontain more than three ATM cells.

Other forms of connection (e.g., VBR, ABR) are also possible besides UBRand CBR; however, these are to be allocated qualitatively to the CBRgroup, and are therefore not dealt with in further detail here. Twogroups are sufficient for the application according to the invention,each connection which has specified a constant transmission rate beingcounted as belonging to the CBR group.

This leads to the following classification of the two kinds oftransmission:

-   -   UBR: AAL5 and regularly packet lengths greater than three ATM        cells.    -   CBR: All other connections, e.g., AAL1 or AAL5 with three or        fewer ATM cells.

The criterion “three ATM cells” for the determination of the UBRconnection can be replaced by an optional other, predeterminable numbergreater than two.

An example of a data transmission system, for which the processaccording to the invention can be used, as illustrated in FIG. 4. Asubscriber's telephone terminal device 9 and data terminal device 13 areconnected via a subscriber circuit 16 to a switching office 20, theanalog or digital signals for the telephone terminal device 9 beingseparated by splitter filters 7, 8 arranged at the ends of a subscriberline circuit 16 from the broadband signals of an ADSL transmission andconducted to, or received by, a subscriber interface (line card) 19. Thedata received by the data terminal device 13 arrives from an ATM network12 which is connected to a broadband-ATM/ADSL line card 11 of theswitching office 20, via the subscriber line circuit 16 into the networktermination unit 10, in which the said data is prepared for the terminaldevice 13. The packetized, asynchronous transmission of data takes placein the ATM process in which, according to requirements, data can be sentand received at a constant (CBR) and also non-constant (UBR) data rate,and in which a buffer with relatively large capacity 11 allocated to theUBR data, and a buffer with relatively small capacity 12 allocated tothe CBR data, are provided. In the reverse direction, transport of thedata from the data terminal device 13 to the network termination unit 10takes place, where the said data is converted into cells and packets andtransmitted toward the ATM network 12.

The process according to the invention for configuring the networktermination unit 10 for packetized, asynchronous ATM transmission ofdata now consists in that the number of the data cells contained in eachsent or received data packet is determined in the network unit 10, andit is determined therefrom whether an ATM connection with constant (CBR)or non-constant (UBR) data rate is present, and that the data packets ofa CBR connection are processed with higher priority than the datapackets of the UBR connection.

For this purpose, the network termination unit 10 comprises according tothe invention a device 14 which, for the determination of the number ofdata cells contained in each data packet, conducts a classification ofthe present ATM connection corresponding to the determined number ofdata cells, and corresponding to this classification, deflects the datapackets either into the buffer with relatively small capacity 12allocated to the CBR data or into the buffer with relatively largecapacity 11 allocated to the UBR data.

For this purpose, each data packet to arrive or to be sent is tested forthis purpose in the device 14; first, the end of a data packet isdetermined by detection of the packet end cell 1′, for which the header2′ is schematically shown in FIG. 3. This header 2′ of the packet endcell 1′ differs from the header of the other cells 1 by the errorrecognition code CRC and a data bit denoted by PTI. As soon as thepacket end cell 1′ has been detected, a statement of the number of cellscontained in the whole packet can be arrived at.

When a data packet is ascertained which contains more than apredeterminable number greater than two of cells, preferably threecells, a UBR data packet is detected, and a CBR data packet in all othercases. The ATM connection is classified as a UBR or a CBR connectioncorresponding to this ascertainment. Thus AAL1 data packets are countedas a CBR transmission without further testing.

It is advantageous if the network termination unit 10 is optionally setin the EPD (Early Packet Discard) mode when a UBR connection isascertained, so that a memory overflow is prevented. In order to makepossible an increase of the correctness of the statement when there areirregularities of the data traffic, a statistical evaluation of severaldata packets can be performed before a decision is arrived at as towhich kind of connection (QoS) is present.

Thus the presence of a UBR or CBR transmission is ascertained only afterevaluation of the results of a predeterminable number of data packets.As indicated in FIG. 4, an effect on the buffers 11, 12 can beundertaken after the ascertainment of the kind of transmission of thedata packets incoming at the present time by means of the device 14 ofthe network termination unit 10 according to the invention.

The data packets detected by the network termination unit 10 as UBR datapackets are fed to a buffer 11 with relatively high storage capacity,and the data packets detected by the network termination unit 10 as CBRdata packets are fed to a buffer 12 with relatively low storagecapacity, where they are buffered for further processing. Anetwork-independent and automatic configuration of the networktermination unit is thereby possible. All connections in the networktermination unit are to be assumed to be CBR connections on switching onor when transmission begins.

1. A method for configuring a network termination unit for asynchronouspacket ATM (Asynchronous Transfer Mode) transmission of data, saidmethod comprising the steps of: dividing the data into data cells;assembling the data cells into packets; transmitting the packets eitherat a constant data rate CBR or at a non-constant data rate UBR, whereinthe data cells of packets are received and sent over the networktermination unit which represents an interface between a transmissionline and a data end device; determining the number of the data cells ineach sent or received data packet in the network termination unit, andit is determined therefrom whether an ATM connection with constant CBRor non-constant UBR data rate is present, the data packets of a CBRconnection being processed with a higher priority then the data packetsof the UBR connection; determining a class of data connection, whereinadaptation layers with different packet lengths are defined for thetransmission of the data packets, wherein, on determination of a datapacket which contains more than a predefined number of cells, saidpredefined number being at least two, a UBR packet is detected, and inall other cases a CBR data packet is detected, and the ATM connection iscorrespondingly classified as a UBR or a CBR connection.
 2. The methodaccording to claim 1, wherein at the beginning of transmission, a CBRconnection is always assumed as the initial value.
 3. The methodaccording to claim 1, wherein the presence of a UBR or CBR connection isdetermined only after the determination of the number of data cells ineach of a plurality of data packets.
 4. The method according to claim 1,wherein, upon establishing a UBR connection, the network terminationunit can optionally be set in the Early Packet Discard (EPD) mode. 5.The method according to claim 1, wherein the data packets detected bythe network termination unit as data packets of a UBR connection are fedto a first buffer and the data packets detected by the networktermination unit as data packets of a CBR connection are fed to a secondbuffer.
 6. A network termination unit for asynchronous packet ATM(Asynchronous Transfer Mode) transmission of data, said networktermination unit comprising: data processing circuitry operative to:divide the data into data cells; assemble the data cells into packets;transmit the packets either at a constant data rate CBR or at anon-constant data rate UBR, wherein the data cells of packets arereceived and sent over the network termination unit which represents aninterface between a transmission line and a data end device; determinethe number of the data cells in each sent or received data packet anddetermine therefrom whether an ATM connection with constant CBR ornon-constant UBR data rate is present, wherein data packets of a CBRconnection are processed with a higher priority than the data packets ofa UBR connection; and determine a class of data connection, whereinadaptation layers with different packet lengths are defined for thetransmission of the data packets, wherein, on determination of a datapacket which contains more than a predefined number of cells, saidpredefined number being at least two, a UBR packet is detected, and inall other cases a CBR data packet is detected, and the ATM connection iscorrespondingly classified as a UBR or a CBR connection.